I wouldn't call Tottenham Court Road a backwater. Yes, it's right at the end of the shopping area, but it's also within easy walking distance of Covent Garden and Leicester Square - both huge tourist areas, then the area to the North/East is more of a business area - which still means a lot of people. The 2017 usage figures actually show Tottenham Court Road as having slightly more entries/exits than Bond Street (41M against 39M).
It's possible there may also be issues about where there is actually space underground to build platforms, but I'm speculating there - I don't know for certain.
The area to the north-east of TCR station (though not the north and the east generally, if that's what you mean by North/East) is not more of a business area. A large proportion of Bloomsbury - which is the quadrant NE of TCR station - is academic institutions, plus the British Museum,
plus (and this is frequently overlooked by planners, including those in the local council, Camden, who should know better [or do know, but don't care]) a large number of homes, many of them of ordinary people who've lived there for much if not all of their (our) lives. [You might remember, for example, that the new British Library was once - 50 years back - due to be built on the 7 acres in front of the BM, until the thousand or so people whose homes were to be flattened ran a successful campaign to stop it.] Given planners' desires to build swish business-friendly infrastructure for visitors and fat-cats, the experience of those of us living in the area is that local transport schemes (both public transport and roads, including the TCR developments) frequently make life worse for those of us who have the temerity to live here - worse in terms of safe and accessible local transport and in terms of other day-to-day local facilities.
According to a recent International Medical Geography Symposium, two of the ten unhealthiest places in the whole of Britain were areas in the immediate vicinity of TCR station. Recent "improvements" in the area have - as far as this local resident's experience goes - only exacerbated that, and the further expansion of TCR station will make our lives even worse.